The invention pertains to a security device for preventing shoplifting consisting of a flexible flat substrate comprising an inductor and a capacitor which form a resonant circuit, the plates of the capacitor being separated by a layer of dielectric material at least one zone of which is designed to make it possible to establish a short-circuit between the plates for a deactivation of the device.
A security device of this kind very often takes the form of a sticker, for example square or rectangular, of a reduced thickness, of the order of a few tenths of a millimeter. This supple security device is designed to be integrated in an invisible manner into products or objects displayed for sale on shop shelves.
In particular, such security devices are used as antitheft protection for shoes and are inserted between two layers of the sole.
When the security device has not been deactivated, the resonant circuit formed by the capacitor and the inductor is in the operating state. When an object fitted with the device passes through the field of action of a detection apparatus, an alarm is triggered.
On the other hand, when the security device has been deactivated, for example at the time of payment for the object, the consumer can cross the zone of action of the detection apparatuses without causing triggering.
The deactivation of the security device is generally obtained by subjecting it to a pulsed emission which, in the zone or zones provided for this purpose of the dielectric layer, causes the establishment of a short-circuit between the plates of the capacitor so that the resonant circuit is no longer operative.
However, it is apparent that such deactivation does not exhibit sufficient reliability. In particular, in the case of shoes, the short-circuit effected by the electrical link between the plates of the capacitor may disappear through breakage of this electrical link when the consumer walks with the shoes. The zone of the sole where the security device is located is in fact subjected to repeated bendings that may provoke the breakage of the electrical link. In the case of such a breakage, the consumer having properly purchased the shoes that he is wearing will trigger an alarm on entering a shop equipped with a detection device for preventing shoplifting. Such untoward triggering is a source of unjustified nuisance for the consumer and should be avoided.
The example has been provided in relation to shoes, but it is clear that other objects or products, equipped with stickers of the kind in question, may be involved.